Flowmeter



Feb. 20, 1962 G. 5. NOVEMBER ETAL 3,021,708

FLOWMETER Filed April 23, 1957 20nd R ff Low-Poss v Recorder 55 ea l ler Fi l ter 4 INVENTOR.

GERALD 3. NOVEMBER FRANK SCHUTE 5 BY flan f a...

3,021,708 FLQETER Gerald S. November, Swampscott, Mass, and Frank Schute, Towson, Md, assignors to the United States of America as represented by the United States Atomic Energy Commission Filed Apr. 23, 1957, Ser. No. 654,627 3 Claims. (Cl. 73-494) This invention relates to a fluid flowmeter and more particularly to a fluid flowrneter employing a resonant cavity.

It is important in the design and operation of a piping system carrying fluid flow to have an indication of flow rate and variations thereof in particular portions of the system. This invention provides a fiowmeter which gives such an indication and utilizes for this purpose a standing Wave set up in the liquid or gas moving through a section of the pipe. The standing wave is set up by abrupt changes in the diameter of the pipe While the amplitude of the standing wave produced thereby is a function of the flow rate. In the practice of this invention we use conventional vibration or pressure pickups and detectors which transform a mechanical movement into an electrical signal.

tude. modulated by a frequency which we designate for convenience the signal frequency. The amplitude of a standing wave represents, as already noted, a particular rate of flow, and variations in the amplitude represent variations in the flow. Such a wave we may consider as consisting of a carrier wave representing a particular rate of flow modulated by deviations which we refer to as the aforementioned signal frequency. If the frequency of the standing wave is considerably greater than the signal frequency the latter will be a sharp indication of variation in flowrate. We have found that a signal frequency of at least aslarge as 500 cycles per second can be readily detected'and measured with this invention. To obtain an indication of the flow rate and variations thereof, the elecrate, i.e., without a zero correction.

Accordingly we include as objects of our invention a new and improved fluid flowmeter; Another object is to provide a fluid flowmeter for indicating fluid flow rate and high frequency variations thereof;

Still a further objectis topfovide a fluid flowmeter for indicating variations in the flow rate up to at least 500 I .cycles per second; 7

a Another object is to provide a fluid flowmeter for indicating fluid flow rate and variations thereof, the meter including a discontinuity as a disturbance creator, a

resonant chamber for standing waves generated by the disturbance, a pickup sensitive to the amplitude of the .standing wave, and an electronic circuit together with a recorder for providing an indication of the fluid flow rate ;and variations thereof; and

A further object of this invention is to provide a fluid flowmeter for measuring fluid flow rate and variations thereof utilizing a discontinuity as a disturbance generator which incorporates a projection in the fluid adjacent the discontinuity as an auxiliary disturbance generator.

Comprehension of this invention and other objects ,thereof Will be better-understood by consideration of the.

accompanying drawing in which:

' v The standing wave sov produced is found to be ampliber 18. The frequency of the standing wave is deterthe sensing section therefrom.

form of an electrical voltage wave. pickups with respect to resonant chamber 18 should pre- Efilfldd Patented Feb. 26, 11562 FIG. 1 is a diagrammatic view of a first embodiment of the resonant cavity of this invention;

FIG. 2 is a diagrammatic view of a second embodiment of the resonant cavity of this invention;

FIG. 3 is a block diagram of an electronic circuit for abstracting the signal from the amplitude-modulated standing wave frequency provided by a pressure wave or by a vibration wave pickup of the sensing section of FIG. 1 or FIG. 2; and

FIG. 4 is a representative portion of a trace on a recorder of variations in a particular flow as provided by the pressure pickup of FIGS. 1 or 2.

in FIGS. 1 and 2 are shown two preferred forms which the sensing section of the flowmeter of this invention may take. The embodiments illustrate auxiliary disturbance generators but it is understood that the sensing sections are operable Without them and the operation of each section will be described as if the auxiliary disturbance generators are not present.

In FIG. 1 numeral 10 indicates generally the sensing section of the embodiment there shown, as it is inserted into a pipe 12 through which a fluid is flowing in the direction of arrows 32. Pipe 12 opens into a cylindrical expansion chamber 14 so that the passage is enlarged abruptly at a plane 16. At the end of chamber 14 opposite pipe 12, the passage through expansion chamber 14 is contracted abruptly at a plane 20 where there is an opening into a coaxial cylindrical resonant chamber 18. The diameter of chamber 18 is larger than the diameter of pipe 12 and is smaller than the diameter of expansion chamber 14. Resonant chamber 18 is connected at its other end to pipe 12 so that the passage through resonant chamber .18 is abruptly reduced at a plane 24 reentering pipe 12. T he entrance port at plane 16 between pipe 12 and expansion chamber 14 is a reflection point for pressure waves present'upstream in pipe 12 and thus serves to isolate sensing section 10 therefrom. The exit port at plane 24 is a reflection point for pressure waves down stream from the sensing section and thus serves to isolate In contact with the outer surface of resonant chamber 18 are placed vibration pickups 26 and 23 located near the midpoint and downstream end thereof respectively as shown. A pressure pickup 30 is placed in contact with the fluid, near the exit port end of resonant chamber 18, as shown.- Since the standing wave in the fluid is a pressure oscillation, any pressure pickup in resonant chamber 18 in contact with the fluid detects the amplitude of the standing wave and converts it into the form of an electrical voltage wave as is understood in the art. Since resonant chamber 18 itself vibrates in response to a pressure oscillation in the fluid there within, a vibration pickup in contact with resonant chamber 18 detects the pressure oscillation, also in the The position of the ferably be placed where the amplitude of the pressure --wave or vibration Wave is at its largest. This provides the largest .amplitude for the carrier frequency. The suitable positions for the pickups can easily be determined in an experimental manner readily apparent to those skilled in the art. A projection identified'as auxiliary disturbance generator 34 may be inserted in the opening between'expansion chamber 14 and resonant chamber 13 at plane 20 to increase the disturbance caused by the discontinuity at plane 2% and reinforce the generation of standing waves.

In the operation of the apparatus of FIG. 1, the flowing fluid enters sensing section 10 by way of pipe 12. The

discontinuity at plane 2d between expansion chamberld and resonant chamber 18 creates a disturbance in the fluid which generates a standing wave in resonant cham- Y 7, 3,021,708 3, I 4, ruined solely: by the :gieernetr y ief the sensing section 19; white the amplitude? bf the :Wa e is? a f nction E of: flute e aria'ti'en's Wave re des'c bediiin terms of i aimum agnalfre :The' output from; fiand passzfilteri 4d is 1 he :preasureosfiliaun whieh transrnits to ew pa'ss fiite r senant cham v i .citified: Ehig'h fre by: making; :the natural: me hani al r que ew.

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area: of a pipe: be abruptly changed to provide :atinuigt to: cause: a: disturbance in: the ing, ecition arrda resonant chamber for st live :to the amplitude elf the; standing Wave zprodiliceid;

thereby and produce on lead 42 an electric voltage wave eflect of the disturbance. having the standing Wave frequency which is amplitude- While the salient features of the present invention modulated by the signal frequency. The amplitude of have been described in detail with respect to two cmthe trace produced by recorder 44 is a direct indication 45 bodiments, it will, of course, be apparent that numerous of the fluid flow. If the trace produced is of constant modifications may be made within the spirit and scope amplitude, thflIl there is 110 Variation in fluid I of the invention, and it is therefore not desired to limit however, as is more Commonly the case, there is a Varitithe invention to the exact details shown except insofar tion in this signal as indicated for example, in the trace as they may b d fi d i th fgllgwing lai shown in FIG. 4, it will be seen that the standing wave W l i fluctuates in amplitude and the variations about some 1, A fl t f i di i fl id fl t d f t imaginary horizontal line Shown) indicate the deviachanges thereof which comprises, in combination: an entions of the fluid flow about the average value represented trance pipe and an exit pipe f Said fl id means y- Thus the information received by h 44 between said pipes for establishing a standing wave hav- PITWides a measure of both flow rate and the changes ing an amplitude which is a function of said fluid flow thercofs already noted, In the event {here no rate, said means consisting of a sensing section having a Changes 111 the flow rate, recorder 44 recelves dlrect cylindrical expansion chamber and a cylindrical resovoltage the magnitude of which indicates the flow rate; nant chamber, said n n chamber having a i and h changes ih the flow rate h P recorder continuity to create a disturbance in said fluid, whereby 44 recelv s a fillchlatlflg Yflltage as Illustrated 4 said disturbance generates said standing wave in said resilldicatlve 0f the Changes In the Y rate above i onant chamber; a detector sensitive to said standing low the normal Iaie- Thus may b6 Considered wave on said resonant chamber to yield an electric voltthat the wave form 1n FIG. 4 consists of a DC. comage wave am litude-modulated by a signal frequency pollehf represehtahve of the 9 flow P reflecting variations in said flow rate, said wave thereby ternatmg component representative of the deviations from containing information concerning said flow rate and th1s normal rate. These deviations may occur at a high said fast changes thereof; a recording Section, said frequency, P to 500 clfcles Per f The use P cording section connected to receive said electric voltresonant cavity 18 to establish the standing wave permits age wave and including an electric circuit to Separate the relatively high frequency Variations in fluid flow to said signal frequency from said wave, said electric cirbe detected. cuit having a band-pass filter and demodulation means A Sensing $605011 of a Second Preferred embodiment of in series, said demodulation means including a rectifier our flowmeter is shown in FIGURE 2 and is indicated and a low-pass filter, and a recorder for indicating said generally by numeral 60. The fluid in this embodiment is flow rate and said fast changes thereof. flowing through a pipe 62 in the direction of the arrows 2. A flowmeter for indicating fluid flow rate and fast 84, and the sensing section 60 is inserted in the pipe. changes thereof which comprises, in combination: an enprovided :epen ito the sen to receireg and: amplify his;

trance pipe and an exit pipe for said fluid flow; a sensing section between said pipes having a cylindrical expansion chamber and a cyEindrical resonant chamber, said expansion chamber having a discontinuity to create a disturbance in said fluid, whereby said disturbance generates a standing wave in said resonant chamber having an amplitude which is a function of said fluid flow-rate; the longitudinal axis of said resonant chamber being parallel to the direction of flow of said fluid through said expansion chamber; a detector sensitive to said standing Wave on said resonant chamber to yield an electric voltage wave amplitude-modulated by a signal frequency reflecting variations in said flow rate, said wave thereby containing information concerning said flow rate and said fast changes thereof; a recording section, said recording section connected to receive said electric voltage wave and including an electric circuit to separate said signal frequency from said wave, said electric circuit having a band-pass filter and demodulation means in series, said demodulation means including a rectifier and a low-pass filter, and a recorder for indicating said flow rate and said fast changes thereof.

3. A fiowmeter for indicating fluid flow rate and fast I longitudinal axis of said resonant chamber being perpendicular to the direction of flow of said fluid through said expansion chamber; a detector sensitive to said standing wave on said resonant chamber to yield an electric Voltage wave amplitude-modulated by a signal frequency reflecting variations in said flow rate, said wave thereby containing information concerning said flow rate and said fast changes thereof; a recording section, said recording section connected to receive said electric voltage wave and including an electric circuit to separate said signal frequency from said wave, said electric circuit having a band-pass filter and demodulation means in series, said demodulation means including a rectifier and a lowpass filter, and a recorder for indicating said flow rate and said fast changes thereof.

References Cited in the file of this patent UNITED STATES PATENTS 1,935,445 Heinz Nov. 14, 1933 2,492,371 Sivian Dec. 27, 1949 2,519,015 Bensen Aug. 15, 1950 2,794,341 Vonnegut June 4, 1957 OTHER REFERENCES Pages -6, A Textbook of Soun by A. T. Wood, published by MacMillan Co. New York in 1955. (QC 225 W6 1955.)

Pages 280-1 The Dynamical Theory of Soun by Horace Lamb, published by Edward Arnold & Co. London in 1925. (QC 223. L2 1925.) 

